Safety and Feasibility of Noninvasive Electromagnetic Stimulation of the Phrenic Nerves

BACKGROUND: Mechanical ventilation is widely used in ICU patients as a lifesaving intervention. Diaphragmatic atrophy and thinning occur from lack of contractions of the diaphragm during me-chanical ventilation. It may prolong weaning and increase the risk of respiratory complications. Noninvasive electromagnetic stimulation of the phrenic nerves may ameliorate the atrophy seen with ventilation. The objective of this study was to show that noninvasive repetitive electromagnetic stim-ulation is safe, feasible, and effective to stimulate the phrenic nerves in both awake individuals and anesthetized patients. METHODS: A single-center study with 10 subjects overall, 5 awake volun-teers and 5 anesthetized subjects. We used a prototype electromagnetic, noninvasive, simultane-ous bilateral phrenic nerve stimulation device in both groups. In the awake volunteers, we assessed time-to-first capture of the phrenic nerves and safety measures, such as pain, discom-fort, dental paresthesia, and skin irritation. In the anesthetized subjects, time-to-first capture as well as tidal volumes and airway pressures at 20%, 30%, and 40% stimulation intensity were assessed. RESULTS: Diaphragmatic capture was achieved in all the subjects within a median (range) of 1 min (1 min to 9 min 21 s) for the awake subjects and 30 s (20 s to 1 min 15 s) for the anesthetized subjects. There were no adverse or severe adverse events in either group, nor any dental paresthesia, skin irritation, or subjective pain in the stimulated area. Tidal volumes increased in all the subjects in response to simultaneous bilateral phrenic nerve stimulation and increased gradually with increasing stimulation intensity. Airway pressures corresponded to sponta-neous breathing of �2 cm H2O. CONCLUSIONS: Noninvasive phrenic nerve stimulation can be safely performed in awake and anesthetized individuals. It was feasible and effective in stimulating the diaphragm by induction of physiologic and scalable tidal volumes with minimum positive airway pressures. Key words: diaphragm; intensive care; muscle atrophy; phrenic nerve stimulation; preven-tion; respiratory muscles; ventilation. [Respir Care 2023;68(5):602-610. & COPY; 2023 Daedalus Enterprises]